Observing H2 Emission in Forming Galaxies

We study the H2 cooling emission of forming galaxies, and discuss their observability using the future infrared facility SAFIR. Forming galaxies with mass >10^11 Msun emit most of their gravitational energy liberated by contraction in molecular hydrogen line radiation, although a large part of thermal energy at virialization is radiated away by the H Ly alpha emission. For more massive objects, the degree of heating due to dissipation of kinetic energy is so great that the temperature does not drop below 10^4 K and the gravitational energy is emitted mainly by the Ly alpha emission. Therefore, the total H2 luminosity attains the peak value of about 10^42 ergs/s for forming galaxies whose total mass 10^11 Msun. If these sources are situated at redshift z=8, they can be detected by rotational lines of 0-0S(3) at 9.7 micron and 0-0S(1) at 17 micron by SAFIR. An efficient way to find such H2 emitters is to look at the Ly alpha emitters, since the brightest H2 emitters are also luminous in the Ly alpha emission.Comment: 20 pages, 7 figures, ApJ accepte

Properties of polycyclic aromatic hydrocarbons in local elliptical galaxies revealed by the Infrared Spectrograph on Spitzer

We performed mid-infrared spectroscopic observations of 18 local dusty elliptical galaxies by using the Infrared Spectrograph (IRS) on board Spitzer. We have significantly detected polycyclic aromatic hydrocarbon (PAH) features from 14 out of the 18 galaxies, and thus found that the presence of PAHs is not rare but rather common in dusty elliptical galaxies. Most of these galaxies show an unusually weak 7.7 um emission feature relative to 11.3 um and 17 um emission features. A large fraction of the galaxies also exhibit H2 rotational line and ionic fine-structure line emissions, which have no significant correlation with the PAH emissions. The PAH features are well correlated with the continuum at 35 um, whereas they are not correlated with the continuum at 6 um. We conclude that the PAH emission of the elliptical galaxies is mostly of interstellar origin rather than of stellar origin, and that the unusual PAH interband strength ratios are likely to be due to a large fraction of neutral to ionized PAHs.Comment: 26 pages, 6 figures, accepted for publication in the Ap

Formation of Sub-galactic Clouds under UV Background Radiation

The effects of the UV background radiation on the formation of sub-galactic clouds are studied by means of one-dimensional hydrodynamical simulations. The radiative transfer of the ionizing photons due to the absorption by HI, HeI and HeII, neglecting the emission, is explicitly taken into account. We find that the complete suppression of collapse occurs for the clouds with circular velocities typically in the range V_c \sim 15-40 km/s and the 50% reduction in the cooled gas mass with V_c \sim 20-55 km/s. These values depend most sensitively on the collapse epoch of the cloud, the shape of the UV spectrum, and the evolution of the UV intensity. Compared to the optically thin case, previously investigated by Thoul & Weinberg (1996), the absorption of the external UV photon by the intervening medium systematically lowers the above threshold values by \Delta V_c \sim 5 km/s. Whether the gas can contract or keeps expanding is roughly determined by the balance between the gravitational force and the thermal pressure gradient when it is maximally exposed to the external UV flux. Based on our simulation results, we discuss a number of implications on galaxy formation, cosmic star formation history, and the observations of quasar absorption lines. In Appendix, we derive analytical formulae for the photoionization coefficients and heating rates, which incorporate the frequency/direction-dependent transfer of external photons.Comment: 38 pages, 16 figures, accepted for publication in Ap

Looking the void in the eyes - the kSZ effect in LTB models

As an alternative explanation of the dimming of distant supernovae it has recently been advocated that we live in a special place in the Universe near the centre of a large void described by a Lemaitre-Tolman-Bondi (LTB) metric. The Universe is no longer homogeneous and isotropic and the apparent late time acceleration is actually a consequence of spatial gradients in the metric. If we did not live close to the centre of the void, we would have observed a Cosmic Microwave Background (CMB) dipole much larger than that allowed by observations. Hence, until now it has been argued, for the model to be consistent with observations, that by coincidence we happen to live very close to the centre of the void or we are moving towards it. However, even if we are at the centre of the void, we can observe distant galaxy clusters, which are off-centre. In their frame of reference there should be a large CMB dipole, which manifests itself observationally for us as a kinematic Sunyaev-Zeldovich (kSZ) effect. kSZ observations give far stronger constraints on the LTB model compared to other observational probes such as Type Ia Supernovae, the CMB, and baryon acoustic oscillations. We show that current observations of only 9 clusters with large error bars already rule out LTB models with void sizes greater than approximately 1.5 Gpc and a significant underdensity, and that near future kSZ surveys like the Atacama Cosmology Telescope, South Pole Telescope, APEX telescope, or the Planck satellite will be able to strongly rule out or confirm LTB models with giga parsec sized voids. On the other hand, if the LTB model is confirmed by observations, a kSZ survey gives a unique possibility of directly reconstructing the expansion rate and underdensity profile of the void.Comment: 20 pages, 9 figures, submitted to JCA

Strong Lensing Analysis of A1689 from Deep Advanced Camera Images

We analyse deep multi-colour Advanced Camera images of the largest known gravitational lens, A1689. Radial and tangential arcs delineate the critical curves in unprecedented detail and many small counter-images are found near the center of mass. We construct a flexible light deflection field to predict the appearance and positions of counter-images. The model is refined as new counter-images are identified and incorporated to improve the model, yielding a total of 106 images of 30 multiply lensed background galaxies, spanning a wide redshift range, 1.0$<$z$<$5.5. The resulting mass map is more circular in projection than the clumpy distribution of cluster galaxies and the light is more concentrated than the mass within $r<50kpc/h$. The projected mass profile flattens steadily towards the center with a shallow mean slope of $d\log\Sigma/d\log r \simeq -0.55\pm0.1$, over the observed range, r$<250kpc/h$, matching well an NFW profile, but with a relatively high concentration, $C_{vir}=8.2^{+2.1}_{-1.8}$. A softened isothermal profile ($r_{core}=20\pm2$\arcs) is not conclusively excluded, illustrating that lensing constrains only projected quantities. Regarding cosmology, we clearly detect the purely geometric increase of bend-angles with redshift. The dependence on the cosmological parameters is weak due to the proximity of A1689, $z=0.18$, constraining the locus, $\Omega_M+\Omega_{\Lambda} \leq 1.2$. This consistency with standard cosmology provides independent support for our model, because the redshift information is not required to derive an accurate mass map. Similarly, the relative fluxes of the multiple images are reproduced well by our best fitting lens model.Comment: Accepted by ApJ. For high quality figures see http://wise-obs.tau.ac.il/~kerens/A168

A bright, dust-obscured, millimetre-selected galaxy beyond the Bullet Cluster (1E0657−56)

This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2008 G. W. Wilson et al. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Deep 1.1 mm continuum observations of 1E0657−56 (the ‘Bullet Cluster’) taken with the millimeter-wavelength camera AzTEC on the 10-m Atacama Submillimeter Telescope Experiment (ASTE), have revealed an extremely bright (S1.1 mm= 15.9 mJy) unresolved source. This source, MMJ065837−5557.0, lies close to a maximum in the density of underlying mass distribution, towards the larger of the two interacting clusters as traced by the weak-lensing analysis of Clowe et al. Using optical–infrared (IR) colours, we argue that MMJ065837−5557.0 lies at a redshift of z= 2.7 ± 0.2. A lensing-derived mass model for the Bullet Cluster shows a critical line (caustic) of magnification within a few arcsec of the AzTEC source, sufficient to amplify the intrinsic millimetre-wavelength flux of the AzTEC galaxy by a factor of ≫20. After subtraction of the foreground cluster emission at 1.1 mm due to the Sunyaev-Zel'dovich effect, and correcting for the magnification, the rest-frame far-IR luminosity of MMJ065837−5557.0 is ≤1012L⊙, characteristic of a luminous infrared galaxy (LIRG). We explore various scenarios to explain the colours, morphologies and positional offsets between the potential optical and IR counterparts, and their relationship with MMJ065837−5557.0. Until higher resolution and more sensitive (sub)millimetre observations are available, the detection of background galaxies close to the caustics of massive lensing clusters offers the only opportunity to study this intrinsically faint millimetre-galaxy population

Compensatory shifts in visual perception are associated with hallucinations in Lewy body disorders

Abstract Visual hallucinations are a common, distressing, and disabling symptom of Lewy body and other diseases. Current models suggest that interactions in internal cognitive processes generate hallucinations. However, these neglect external factors. Pareidolic illusions are an experimental analogue of hallucinations. They are easily induced in Lewy body disease, have similar content to spontaneous hallucinations, and respond to cholinesterase inhibitors in the same way. We used a primed pareidolia task with hallucinating participants with Lewy body disorders (n = 16), non-hallucinating participants with Lewy body disorders (n = 19), and healthy controls (n = 20). Participants were presented with visual “noise” that sometimes contained degraded visual objects and were required to indicate what they saw. Some perceptions were cued in advance by a visual prime. Results showed that hallucinating participants were impaired in discerning visual signals from noise, with a relaxed criterion threshold for perception compared to both other groups. After the presentation of a visual prime, the criterion was comparable to the other groups. The results suggest that participants with hallucinations compensate for perceptual deficits by relaxing perceptual criteria, at a cost of seeing things that are not there, and that visual cues regularize perception. This latter finding may provide a mechanism for understanding the interaction between environments and hallucinations